In semiconductor integrated circuit (IC) fabrication, metal lines are deposited to interconnect IC components and to connect IC components to pads. The metal lines are formed by physical deposition (such as by sputtering) of a layer of metal (such as aluminum or an aluminum-copper alloy). Photoresist is applied to the metal layer to define a pattern for forming lines that interconnect the desired components of the IC. One common apparatus used for such etching is the Applied Materials MxP Centura.
The "metal layer" is typically not just a layer of aluminum or aluminum-copper alloy, but rather more typically is a composite stack of different layers. FIG. 1 shows such as prior art composite metal layer. The metal layer 101 comprises a bottom titanium/titanium nitride layer 103, an aluminum or copper layer 105, and a top titanium/titanium nitride layer 107. The purpose of the titanium/titanium nitride layers 103 and 107 are to act as both an adhesion layer and a diffusion barrier layer.
The use of this composite metal stack 101 is currently common practice in the semiconductor industry. As the widths of the metal lines decrease, the demands of the photolithography process require the use of an anti-reflection coating (ARC). It has been found however that the ARC, particularly organic ARC's, react adversely with the titanium/titanium nitride layer 107 to form micro masks that affect the metal etching. This may lead to yield problems such as metal line shorting.
Thus, what is needed is a method of preventing the organic ARC's from reacting with the titanium/titanium nitride layer 107.